Rotary air motor

ABSTRACT

In a rotary motor a plurality of radially-directed cylinders are located on a stator and include reciprocating pistons whose outer ends react with a cam track defined on the inner surface of a rotatable output member mounted coaxially with the stator, the pistons being driven pneumatically in a predetermined sequence by means of an air distribution arrangement in which two cooperating valve plates, one stationary and the other movable with the output member, operate between sources of air relatively high and low pressure and cylinder ports in the stator communicating with said cylinders.

Unite States Patent 11 1 1111 3,780,624 Webb Dec. 25, 1973 ROTARY A MOTOR 3,056,357 10/1962 Bohnhoff 91/487 [75] Inventor: Frank Alan Webb, Twickenham, FOREIGN PATENTS 0 APPLICATIONS England 927,926 6/1963 Great Britain 91/180 [73] Assignee: Martonair Limited, Middlesex,

England Primary Examiner-William 1.. Freeh [22] Filed: 12, 1971 Assistant ExaminerG regory L. LaPointe Attorney-John Mawhinney et al. [21] Appl. No.: 171,236

30 F A h P D [57] ABSTRACT ti ta 1 S :relgn Pp ca on y a In a rotary motor a plurality of radially-directed cylinept. 1, 1970 Great Britam 40,326/70 ders are located on a Stator and include reciprocating pistons whose outer ends react with a cam track de- [52] 11.8. C1 91/491, 91/180, 91/498 fined on the inner Surface of a rotatable Output [51] Int. Cl. F0lb 13/00 ber mounted coaxrally with the stator, the pistons [58] Field of Search 91/180, 498, 487, 1 1

91/488 501 506 491 being driven pneumatically m a predetermlned sequence by means of an air distribution arrangement in which two co-operating valve plates, one stationary [56] References Cited and the other movable with the output member, oper- UNITED STATES PATENTS ate between sources of air relatively high and low 3,046,950 7/1962 Smith 91/498 pressure and cylinder ports in the stator communicat- 2,972,962 2/1961 Douglas 91/488 ing with said cylinders. 3,283,668 11/1966 L0uhio..... 91/180 3,603,211 9/1971 Firth 91/180 9 Claims, 5 Drawing Figures PATENTED 3,780,624

FIG.I.

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, I I 1 l 1 L [ML 1 l L INVENTOR FRANK ALM \A/Ea ATTORNEY ROTARY AIR MOTOR This invention relates to a rotary motor powered by air or some other suitable gas and for convenience termed a rotary air motor. A particular application of some embodiments of the present invention is in a pneumatic hoist.

According to the invention a rotary air motor comprises a stator and an output member arranged for relative rotation about a common axis of rotation, there being provided a plurality of cylinders integral with the stator and angularly displaced with respect to said axis of rotation, a piston reciprocatably mounted within each of said cylinders, said output member being in the form of a hollow, generally cylindrical drum provided with an inner surface defining a cam track arranged for co-operative engagement with said pistons and air distributor means arranged to admit air under pressure to said cylinders in a predetermined sequence whereby said pistons are cyclically urged into engagement with said track to produce reaction forces which tend to rotate said output member relative to the stator about said axis of rotation.

Preferably, cylinder ports separately communicating with individual cylinders are included in said stator and said distributor means includes a rotary valve plate connected to said output member and provided with a plurality of valve ports arranged for sequential registration with said cylinder ports, the stator being so formed in the region of said rotary valve plate that predetermined valve ports always communicate with air under pressure and the remaining ports always communicate with air under relatively low pressure.

Desirably, there is provided a stationary valve plate corresponding to said rotary valve plate and including a plurality of apertures mutually aligned with said cylinder ports, the rotary and stationary valve plates being provided on adjacent contacting faces with a surface finish such that a substantially gas-tight seal is produced, without the need for any additional sealing.

In some embodiments of the invention said cam track includes a plurality of inwardly-projecting lobes alternating with depressions, sloping boundary surfaces between the lobes and depressions having a gradient such that equal changes in angular position of the output member relative to the stator produce corresponding equal linear displacements of the pistons in their respective cylinders. Desirably a roller follower is mounted on the outer end of each piston for engagement with said cam track.

Conveniently, a pair of axially spaced flanges each provided with radial grooves on their mutually facing surfaces are attached to the stator, there being provided additional rollers fitted to each piston and located in said radial grooves, whereby the reciprocating movement of each piston is constrained along a radial direction with respect to the axis of rotation.

Desirably, the numbers of valve ports exceeds the numbers of cylinder ports by unity, said valve ports and cylinder ports being equally spaced about said axis of rotation and the number of cam lobes and depressions exceeds the number of pistons.

In one embodiment of the invention, for example, there are provided six identical pistons and seven each of the cam lobes, cam depressions and valve ports, the stationary and rotary valve plates being arranged whereby, at any one time during operation of the motor, three adjacent cylinders are subjected to air under pressure and the remaining three cylinders are subjected to air at a relatively low pressure.

Desirably, there is provided spring means for biasing each piston into engagement with the cam track.

The invention further provides a pneumatic hoist including a rotary air motor according to any of the eight immediately preceding paragraphs wherein the output member comprises a winding drum with helically grooved outer surface, there being provided a winding cable located in said helical groove for supporting a load whereby rotation of the winding drum serves to wind-on or unwind the cable with respect thereto, according to the sense of rotation, and a load attached to the cable may be respectively raised and lowered.

There now follows a description of a particular embodiment of the invention by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 shows a sectional, part cut-away view of a pneumatic hoist incorporating a rotary air motor;

FIG. 2 shows a generally sectional view taken along the line 22 in FIG. 1, but partly cut-away and on an enlarged scale for clarity;

FIG. 3 shows on the same scale as FIG. 2, a rotary valve plate incorporated in the pneumatic hoist shown in FIGS. 1 and 2;

FIG. 4 shows, in the same scale as FIG. 1, an elevation of the pneumatic hoist mounted for operation, and

FIG. 5 shows a side elevation of FIG. 4.

Referring to FIG. 1, a pneumatic hoist includes a radial piston type of rotary air motor in which a central stator 12 of generally circular section is provided with six radially-directed cylinders 14 each receiving a corresponding piston 15 slidably mounted therein with a resilient annular sealing ring 16 located between each piston 15 and the walls of the respective cylinder 14. The six pistons 15 interact with an output member in the form of a hollow cylindrical winding drum 19 with a profiled inner surface defining a cam track 20 with a series of seven equally-spaced cam lobes 21 alternating with a series of seven equally-spaced cam troughs or depressions 22.

Referring to FIG. 2, the outer end of each piston 15 engages the cam track 20 through a central roller 27 of a set of three rollers coaxially-mounted upon an axle 25 which is supported from forked limbs 28 integral with the piston 15. Two outer guide rollers 26 are located within corresponding radially-directed guideways 43 in each of two axially-spaced support flanges 44 which are attached to the stator 12. This arrangement serves to locate the pistons 15 in their movement from their fully retracted to fully extended positions. The pistons 15 are biassed outwards from the centre of the stator 12 by coil springs 31 located within the cylinders 14. Each cylinder 14 communicates, through a cylinder port 23, with coaxial tubes 39, 38 connected respectively to relatively high and low pressure sources of air. The tube 38 connected to the low pressure region is termed exhaust and the tube 39 connected to the high pressure region is termed inlet. The winding drum 19 is free to rotate about the stator 12 and is supported therefrom by means of two axially-spaced sets of ball bearings 48, 49. The outer curved surface of the winding drum is provided with a helical groove 41 of suitable section to receive a winding cable 57 which is attached at one end 37 to a casing 42 which partially encloses the winding drum 19 and is rigidly attached to the stator 12. The winding cable 57 extends from the fixed end 37 around a pulley 58 of a hook assembly 59 (not shown in full) and continues back around the winding drum 19 along the helical groove 41 and terminates therein at a place not shown. Rotation of the winding drum 19 serves to wind or unwind the cable 57 there- .from, according to the direction of rotation, resulting in a corresponding raising or lowering of the hook assembly 59 and any load suspended therefrom.

The radial piston air motor is powered by compressed air supplied, by means not shown, to the inlet 39 from where it is distributed to all six cylinders by a rotary valve air distributor comprising a rotary annular valve plate 65 and a stationary valve plate 35 shown in FIG. 3. The stationary valve plate 35 is provided with six circumferentially-spaced apertures of corresponding cross-section to the six cylinder ports 23. The rotary valve plate 65 is provided wtih fourteen valve ports seven of which comprise apertures 32 of corresponding cross-sectional shape and size and equally-spaced about the common axis of rotation of the stator and winding drum 19. Alternating with these apertures 32 are a further seven valve ports in the form of transverse slots 66 each leading from the inside to the outside of the rotary valve plate 65. The slotted face of the rotary valve plate 65 including these transverse slots 66 is machined and polished to a high degree of surface flatness. The corresponding face of the stationary valve plate35 is similarly finished whereby, when the rotary and stationary valve plates are adjacently arranged with their polished faces mating, there is produced a substantially gas-tight joint 68 which is maintained when there is relative rotation therebetween, without the need for any additional sealing gland. The side of the stationary valve plate 35 opposite the polished flat face is adjacent the cylinder ports 23 and an annular sealing gland 33 serves to seal the valve plate 35 to the body of the stator 12.

The rotary valve plate 65 rotates with the winding drum l9, and in so doing successively aligns apertures 32 and slots 66 with the apertures in the stationary valve plate 35 and the cylinder ports 23. The inlet 39 and exhaust 38 are separated by a plate integral with the stator 12 and communication between them and the cylinder ports 23 is controlled by the relative angular positions of the stationary and rotary valve plates 35 and 65 respectively. The stator 32 is so formed in the region of the valve plate 35 so that the apertures 32 in the valve plate 65 always communicate directly with the inlet 39 through a passageway 70, whilst the slots 66 always communicate directly with exhaust 38 through a passageway 69. Consequently, as the winding drum 19 and rotary valve plate 65 rotate together, a certain number of cylinder ports 23 are connected to the inlet 39 and the remaining cylinder ports 23 are connected to the exhaust 38. In this example the relationship between the apertures 32, slots 66 and cylinder ports 23 is such that, at any one time, three adjacent cylinders H are connected to the inlet 39 while the three remaining adjacent cylinders 14 are connected to the exhaust 33. The pressure of air at the inlet is such that, when communicated to a cylinder 14, the respective piston 15 is urged outwards against the cam track and the reaction therebetween has a tangential component which tends to rotate the winding drum 19 about the stator 12. The actions of the pistons 15 are co-operative in that at any one time the rollers 27 of each piston are at a different position on the cam track 20 and the respective cylinders are at correspondingly different stages in their operating cycles. Thus at any one time, for the three cylinders 14 subjected to the inlet pressure, the respective pistons 15 are at different displacements from the centre of the stator 12. As one such piston 15 completes its outward or power stroke it is then subjected to the exhaust pressure, by virtue of the movement of the rotary valve plate 65, and returns to its retracted position driving the air in its associated cylinder 14 into the exhaust 38. Simultaneously, the diametrically opposite piston 15 has just completed its return or inward stroke and is then subjected to the inlet pressure urging it outwards on its power stroke. The flanks of the cam lobes 21 are acted upon by the pistons 15 on their power strokes and act back on the pistons 15 to produce the latters return strokes.

The flanks between the cam lobes 21 and cam troughs 22 are of constant rate, that is to say equal angular displacements of the cam track 20 relative to the stator 12 produce corresponding equal changes in the linear displacement a piston 15 in its cylinder 14.

In practice, the supply of compressed air to the inlet 39 may be controlled by a manually operated control which incorporates, say raise, hold and lower control buttons. Actuation of a lift button would allow compressed air into the inlet 39 and with the result that the winding drum 19 rotates, as previously explained, until the hold button is actuated whereupon the supply of compressed air is shut off with the exhaust 38 blocked so that any load on the winding drum 19 from the hook assembly 59 is balanced by the pressure of the air trapped in the three cylinders connected to inlet. Actuation of the lower button opens the inlet 39 and allows the cylinders 14 to discharge'air therethrough and, when the pressure falls sufficiently, the winding drum 19 rotates in the reverse direction under the action of the load. During lowering of the load the pneumatic hoist acts as a compressor and the rate of lowering depends upon the flow of air possible through the inlet 39 which is in turn controlled by the lower button control. For safety reasons an automatic hold device is incorporated into the control unit to prevent the load falling out of control in the event of failure of the compressed air supply. lf required, the control unit may be adapted to supply any one of three different pressures to the inlet 39, each pressure being determined by a particular load requirement. With one pressure selected, the normal raise, hold and lower controls may be used as previously described. With the hold condition selected the pneumatic hoist will balance the particular load which can then readily be moved manually without recourse to the control unit.

FIGS. 4 and 5 shows a pneumatic hoist supporting a hook assembly 59 and mounted on a guide rail 60. The outer casing 42 of the pneumatic hoist is provided with two pivot pins 45 which are received in respective brackets 55 attached to U-shaped arms 56 the limbs of which support wheels 50 which run along lower flanges of the guide rail 66. The inlet 39 and exhaust 38 are connected to relatively high and low pressure supplies respectively by means, for example, flexible air hoses, not shown. The pneumatic hoist is thus free to travel along the guide rail 60.

What I claim as my invention and desire to secure by Letters Patent of the United States is:

l. A rotary air motor comprising a stator and a hollow generally cylindrical output member arranged for relative rotation about a common axis of rotation, there being provided a plurality of cylinders integral with the stator and angularly displaced with respect to said axis of rotation, a piston reciprocably mounted within each of said cylinders, a cam track defined by an inner curved surface of said output member for co-operative engagement with said pistons, a plurality of axially and radially-extending cylinder ports in said stator separately communicating with individual cylinders, a rotary valve plate drivably connected to said output member, a plurality of axially and radially-extending valve ports in said rotary valve plate arranged for movement into sequential registration and communication wtih said cylinder ports across relatively movable seal surfaces of the stator and the rotary valve plate around their respective ports, the stator being so formed in the region of said rotary valve plate that predetermined valve ports always communicate with air under pressure and the remaining valve ports always communicate with air under relatively low pressure whereby to admit air under pressure to said cylinders in a predetermined sequence to urge said pistons cyclically into engagement with said track to produce reaction forces which tend to rotate said output member relative to the stator about said axis of rotation.

2. A rotary air motor, as claimed in claim 1, wherein cylinder ports separately communicating with individual cylinders are included in said stator and said air distributor means includes a rotary valve plate connected to said output member and provided with a plurality of valve ports arranged for sequential registration with said cylinder ports, the stator being so formed in the region of said rotary valve plate that predetermined valve ports always communicate with air under relatively low pressure.

3. A rotary air motor, as claimed in claim 1, wherein there is provided a stationary valve plate corresponding rotary and stationary valve plates being provided on adjacent contacting seal surfaces with a surface finish such that a substantially gas-tight seal is produced, without the need for any additional sealing.

4. A rotary air motor, as claimed in claim 1, wherein said cam track includes a plurality of inwardly projecting lobes alternating with depressions, sloping boundary surfaces between the lobes and depressions having a gradient such that equal changes in angular position of the output member relative to the stator produce corresponding equal linear displacements of the pistons in their respective cylinders.

5. A rotary air motor, as claimed in claim 1, wherein a roller follower is mounted on the outer end of each piston for engagement with said cam track.

6. A rotary air motor, as claimed in claim 5, wherein a pair of axially spaced flanges each provided with radial grooves on their mutually facing surfaces are attached to the stator, there being provided additional rollers fitted to each piston and located in said radial grooves, whereby the reciprocating movement of each piston is constrained along a radial direction with respect to the axis of rotation.

7. A rotary air motor, as claimed in claim 4, wherein the numbers of valve ports exceeds the numbers of cylinder ports by unity, said valve ports and cylinder ports being equally spaced about said axis of rotation and the number of cam lobes and depressions exceeds the number of pistons.

8. A rotary air motor, as claimed in claim 4, wherein there are provided six identical pistons and seven each of the cam lobes, cam depressions and valve ports, the stationary and rotary valve plates being arranged whereby, at any one time during operation of the motor, three adjacent cylinders are subjected to air under pressure and the remaining three cylinders are subjected to air at a relatively low pressure.

9. A rotary air motor, as claimed in claim 1, wherein there is provided spring means for biasing each piston to said rotary valve plate and including a plurality of into engagement with the cam track. 

1. A rotary air motor comprising a stator and a hollow generally cylindrical output member arranged for relative rotation about a common axis of rotation, there being provided a plurality of cylinders integral with the stator and angularly displaced with respect to said axis of rotation, a piston reciprocably mounted within each of said cylinders, a cam track defined by an inner curved surface of said output member for co-operative engagement with said pistons, a plurality of axially and radially-extending cylinder ports in said stator separately communicating with individual cylinders, a rotary valve plate drivably connected to said output member, a plurality of axially and radially-extending valve ports in said rotary valve plate arranged for movement into sequential registratioN and communication wtih said cylinder ports across relatively movable seal surfaces of the stator and the rotary valve plate around their respective ports, the stator being so formed in the region of said rotary valve plate that predetermined valve ports always communicate with air under pressure and the remaining valve ports always communicate with air under relatively low pressure whereby to admit air under pressure to said cylinders in a predetermined sequence to urge said pistons cyclically into engagement with said track to produce reaction forces which tend to rotate said output member relative to the stator about said axis of rotation.
 2. A rotary air motor, as claimed in claim 1, wherein cylinder ports separately communicating with individual cylinders are included in said stator and said air distributor means includes a rotary valve plate connected to said output member and provided with a plurality of valve ports arranged for sequential registration with said cylinder ports, the stator being so formed in the region of said rotary valve plate that predetermined valve ports always communicate with air under relatively low pressure.
 3. A rotary air motor, as claimed in claim 1, wherein there is provided a stationary valve plate corresponding to said rotary valve plate and including a plurality of apertures mutually aligned with said cylinder ports, the rotary and stationary valve plates being provided on adjacent contacting seal surfaces with a surface finish such that a substantially gas-tight seal is produced, without the need for any additional sealing.
 4. A rotary air motor, as claimed in claim 1, wherein said cam track includes a plurality of inwardly projecting lobes alternating with depressions, sloping boundary surfaces between the lobes and depressions having a gradient such that equal changes in angular position of the output member relative to the stator produce corresponding equal linear displacements of the pistons in their respective cylinders.
 5. A rotary air motor, as claimed in claim 1, wherein a roller follower is mounted on the outer end of each piston for engagement with said cam track.
 6. A rotary air motor, as claimed in claim 5, wherein a pair of axially spaced flanges each provided with radial grooves on their mutually facing surfaces are attached to the stator, there being provided additional rollers fitted to each piston and located in said radial grooves, whereby the reciprocating movement of each piston is constrained along a radial direction with respect to the axis of rotation.
 7. A rotary air motor, as claimed in claim 4, wherein the numbers of valve ports exceeds the numbers of cylinder ports by unity, said valve ports and cylinder ports being equally spaced about said axis of rotation and the number of cam lobes and depressions exceeds the number of pistons.
 8. A rotary air motor, as claimed in claim 4, wherein there are provided six identical pistons and seven each of the cam lobes, cam depressions and valve ports, the stationary and rotary valve plates being arranged whereby, at any one time during operation of the motor, three adjacent cylinders are subjected to air under pressure and the remaining three cylinders are subjected to air at a relatively low pressure.
 9. A rotary air motor, as claimed in claim 1, wherein there is provided spring means for biasing each piston into engagement with the cam track. 